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Research Papers: Gas Turbines: Structures and Dynamics

Subsynchronous Vibration Patterns Under Reduced Oil Supply Flow Rates

[+] Author and Article Information
Bradley R. Nichols

Rotating Machinery and Controls Laboratory,
Department of Mechanical and
Aerospace Engineering,
University of Virginia,
Charlottesville, VA 22904
e-mails: brn7 h@virginia.edu;
brad.nichols@rotorsolution.com

Roger L. Fittro

Rotating Machinery and Controls Laboratory,
Department of Mechanical and
Aerospace Engineering,
University of Virginia,
Charlottesville, VA 22904
e-mail: fittro@virginia.edu

Christopher P. Goyne

Rotating Machinery and Controls Laboratory,
Department of Mechanical and
Aerospace Engineering,
University of Virginia,
Charlottesville, VA 22904
e-mail: goyne@virginia.edu

1Corresponding author.

2Present address: Rotor Bearing Solutions International, Charlottesville, VA 22911.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 11, 2017; final manuscript received August 31, 2017; published online July 9, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(10), 102503 (Jul 09, 2018) (8 pages) Paper No: GTP-17-1346; doi: 10.1115/1.4038363 History: Received July 11, 2017; Revised August 31, 2017

Reduced oil supply flow rates in fluid film bearings can cause cavitation, or lack of a fully developed hydrodynamic film layer, at the leading edge of the bearing pads. Reduced oil flow has the well-documented effects of higher bearing operating temperatures and decreased power losses; however, little experimental data of its effects on system stability and performance can be found in the literature. This study looks at overall system performance through observed subsynchronous vibration (SSV) patterns of a test rig operating under reduced oil supply flow rates. The test rig was designed to be dynamically similar to a high-speed industrial compressor. It consists of a flexible rotor supported by two tilting pad bearings in vintage, flooded bearing housings. Tests were conducted over a number of supercritical operating speeds and bearing loads, while systematically reducing the oil supply flow rates provided to the bearings. A low amplitude, broadband SSV pattern was observed in the frequency domain. During supercritical operation, a distinctive subsynchronous peak emerged from the broadband pattern at approximately half of the running speed and at the first bending mode of the shaft. Under lightly loaded conditions, the amplitude of the subsynchronous peak increased dramatically with decreasing oil supply flow rate and increasing operating speed. Under an increased load condition, the subsynchronous peak was largely attenuated. A discussion on the possible sources of this SSV including self-excited instability and pad flutter forced vibration is provided with supporting evidence from thermoelastohydrodynamic (TEHD) bearing modeling results.

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References

Newkirk, B. L. , and Taylor, H. D. , 1925, “ Shaft Whipping Due to Oil Action in Journal Bearings,” Gen. Electr. Rev., 28(8), pp. 549–568. https://dyrobes.com/wp-content/uploads/2012/12/Shaft-Whipping-Action-Due-to-Oil-Action-in-Journal-Bearings-Newkirk-Taylor-1925.pdf
Adams, M. L. , and Payandeh, S. , 1983, “ Self-Excited Vibration of Statically Unloaded Pads in Tilting-Pad Bearings,” ASME J. Lubr. Technol., 105(3), pp. 377–383. [CrossRef]
DeCamillo, S. M. , He, M. , and Cloud, C. H. , 2008, “ Journal Bearing Vibration and SSV Hash,” 37th Turbomachinery Symposium, Houston, TX, Sept. 8–11, pp. 11–22.
Nicholas, J. C. , 2003, “ Tilting Pad Journal Bearings With Spray-Bar Blockers and By-Pass Cooling for High Speed, High Load Applications,” 32nd Turbomachinery Symposium, Houston, TX, Sept. 8–11, pp. 27–38.
Brockwell, K. , Dmochowski, W. , and DeCamillo, S. , 1994, “ Analysis and Testing of LEG Tilting Pad Journal Bearing-A New Design for Increasing Load Capacity, Reducing Operating Temperatures and Conserving Energy,” 23rd Turbomachinery Symposium, Dallas, TX, Sept. 13–15, pp. 43–56.
DeCamillo, S. , and Brockwell, K. , 2001, “ A Study of Parameters That Affect Pivoting Shoe Journal Bearing Performance in High-Speed Turbomachinery,” 30th Turbomachinery Symposium, Houston, TX, Sept. 17–20, pp. 9–22.
Dmochowski, W. , and Blair, B. , 2006, “ Effect of Oil Evacuation on the Static and Dynamic Properties of Tilting Pad Journal Bearings,” Tribol. Trans., 49(4), pp. 536–544. [CrossRef]
Cloud, C. H. , 2007, “ Stability of Rotors Supported on Tilting-Pad Journal Bearings,” Ph.D. dissertation, University of Virginia, Charlottesville, VA.
Nicholas, J. C. , 1994, “ Tilting Pad Bearing Design,” 23rd Turbomachinery Symposium, Dallas, TX, Sept. 13–15, pp. 179–194.
He, M. , 2003, “ Thermoelastohydrodynamic Analysis of Fluid Film Journal Bearings,” Ph.D. dissertation, University of Virginia, Charlottesville, VA.
He, M. , Allaire, P. E. , Barrett, J. , and Nicholas, J. C. , 2005, “ Thermohydrodynamic Modeling of Leading-Edge Groove Bearings Under Starved Conditions,” Tribol. Trans., 48(3), pp. 362–369. [CrossRef]
Taura, H. , and Tanaka, M. , 2004, “ Self-Excited Vibration of Elastic Rotors in Tilting Pad Journal Bearings,” Eighth International Conference on Vibrations in Rotating Machinery, Swansea, UK, Sept. 7–9, pp. 35–43.

Figures

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Fig. 2

Test bearing drawing [8]

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Fig. 3

Ramp-up waterfall plot 1000–12,000 rpm, nominal flow rate, low load

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Fig. 4

Frequency response versus running speed 0–200 Hz, nominal flow rate, low load

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Fig. 5

Frequency response versus running speed 40–100 Hz, nominal flow rate, low load

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Fig. 6

Frequency response versus running speed 0–200 Hz, nominal flow rate, high load

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Fig. 7

Maximum SSV displacement versus running speed, nominal flow rate

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Fig. 8

Frequency response versus oil supply flow rate 0–200 Hz, 9000 rpm, low load

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Fig. 9

Frequency response versus oil supply flow rate 0–200 Hz, 11,000 rpm, low load

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Fig. 10

Maximum SSV displacement versus flow rate, low load

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Fig. 11

Maximum SSV displacement versus flow rate, medium load

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Fig. 12

Frequency response versus oil supply flow rate 0–200 Hz, 11,000 rpm, high load

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Fig. 13

Maximum SSV displacement versus flow rate, high load

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Fig. 14

Predicted pressure profiles versus speed, nominal flow rate, low load (581 kPa max)

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Fig. 15

Predicted pressure profiles versus flow rate, 11,000 rpm, low load (627 kPa max)

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Fig. 16

Predicted pressure profiles versus speed, nominal flow rate, high load (1089 kPa max)

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Fig. 17

Predicted pressure profiles versus flow rate, 11,000 rpm, high load (1034 kPa max)

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